Find all topics related to a post id using CakePHP

I'm trying to write a model method that will pull topics attached to a post. The DB setup is as follows:

Post
 id
 title
 
 Topic
 id
 title
 
 Post_Topic
 id
 post_id
 topic_id
 

and the example method...

public function getPostTopics($postId)
 {   
     $topics = $this->find('all', ...
     return $topics;
 }
 

What I need to do is find the relationships in the DB and then store them in the following format for the return e.g. tag1, tag2, tag3.

Can anyone help me out?

Here are the associations:

Post.php
 class Post extends AppModel
 {
     public $name = 'Post';
 
     public $belongsTo = 'User';
 
     public $hasMany = array('Answer');
 
     // Has many topics that belong to topic post join table... jazz
     public $hasAndBelongsToMany = array(
         'Topic' => array('with' => 'TopicPost')
     );
 }
 
 Topic.php
 class Topic extends AppModel
 {
     public $hasMany = array(
         'TopicPost'
     );
 }
 
 TopicPost.php
 class TopicPost extends AppModel {
     public $belongsTo = array(
         'Topic', 'Post'
     );
 }
 

and for an example of how it's saved into the Database (to give an idea of how a function in the model works) in the first place (courtesy of another helpful person on SO)

public function savePostTopics($postId, $topics)
{
// Explode the topics by comma, so we have an array to run through
$topics = explode(',', $topics);
// Array for collecting all the data
$collection = array();

foreach($topics as $topic)
 {
     // Trim it so remove unwanted white spaces in the beginning and the end.
     $topic = trim($topic);
 
     // Make it all lowercase for consistency of tag names
     $topic = strtolower($topic);
 
     // Check if we already have a topic like this
     $controlFind = $this->find(
         'first',
         array(
             'conditions' => array(
                 'title' => $topic
             ),
             'recursive' => -1
         )
     );
 
     // No record found
     if(!$controlFind)
     {
         $this->create();
         if(
             !$this->save(
                 array(
                     'title' => $topic
                 )
             )
         )
         {
             // If only one saving fails we stop the whole loop and method.
             return false;
         }
         else
         {
             $temp = array(
                 'TopicPost' => array(
                     'topic_id' => $this->id,
                     'post_id' => $postId
                 )
             );
         }
     }
     else
     {
         $temp = array(
             'TopicPost' => array(
                 'topic_id' => $controlFind['Topic']['id'],
                 'post_id' => $postId
             )
         );
     }
 
     $collection[] = $temp;
 }
 
 return $this->TopicPost->saveMany($collection, array('validate' => false));
 

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